Infiltrations 1 & 2

What is infiltration in pathology?

The accumulation of material within tissues, which can be exogenous or endogenous, intracellular or extracellular, and located in the cytoplasm (lysosomes) or nucleus.

What are the main types of infiltrations?

• Normal or increased production with decreased metabolism (e.g., fatty liver).

• Defective enzymatic degradation or storage in an insoluble form (e.g., storage diseases, cell damage, fatty liver).

• Abnormal substance storage with no degradative pathway (e.g., carbon, viral inclusions).

• Reduced removal of a substance from a cell (e.g., apolipoproteins in fatty liver).

What are the three main causes of storage diseases?

• Excess supply – Too much of a substance enters the cell.

• Defective cell mechanism – Enzymatic or metabolic pathways fail.

• Defective transport out – The cell cannot remove the stored material.

Where does calcification normally occur, and what does pathological calcification indicate?

Calcification normally occurs in bones and teeth. Deposition in soft tissues is pathological and can be dystrophic (localized, normal blood calcium) or metastatic (systemic, high blood calcium or phosphate).

What regulates calcium and phosphate homeostasis in the body?

Plasma Ca²⁺ and PO₄²⁻ levels are regulated by:

• Parathyroid hormone (PTH) – increases Ca²⁺, decreases PO₄²⁻

• 1,25-dihydroxyvitamin D – increases Ca²⁺ and PO₄²⁻ absorption

• Calcitonin – decreases Ca²⁺ by suppressing osteoclastic activity

How does PTH regulate calcium levels?

• Bone: Activates osteoclasts → releases Ca²⁺ and PO₄²⁻

• Kidney: Increases Ca²⁺ reabsorption, decreases PO₄²⁻ reabsorption

• Intestine: Increases Ca²⁺ absorption via vitamin D activation

What are the roles of Vitamin D (1,25-dihydroxyvitamin D)?

• Increases Ca²⁺ and PO₄²⁻ absorption from intestines

• Stimulates bone resorption to release Ca²⁺ and PO₄²⁻

• Enhances PO₄²⁻ reabsorption in kidneys

• Regulated by negative feedback

What triggers calcitonin secretion, and what does it do?

• Trigger: Increased plasma Ca²⁺

• Effect: Suppresses osteoclastic bone resorption, reducing blood Ca²⁺ levels

What is dystrophic calcification, and how does it appear?

• Occurs in dead or dying tissue

• Blood calcium levels are normal

• Gross: White, gritty, firm

• Microscopic: Basophilic crystals

What is metastatic calcification, and what are its causes?

• Systemic – occurs due to high serum Ca²⁺ and/or PO₄²⁻

• Causes:

  • Primary hyperparathyroidism (parathyroid tumors)

  • Secondary hyperparathyroidism (renal failure, nutritional)

  • Vitamin D toxicosis (excess supplementation, toxic plants, cholecalciferol rodenticides)

How does secondary hyperparathyroidism lead to metastatic calcification?

• Chronic renal failure → phosphate retention → low serum Ca²⁺

• Triggers excess PTH production → bone resorption → Ca²⁺ release → tissue deposition

What are common sites of metastatic calcification?

• Alveolar walls

• Ribs

• Blood vessel walls

What are the three main components of hemoglobin (Hb)?

1. Heme

2. Globin

3. Iron (Fe)

What is hemolysis, and what are its types?

Hemolysis is the breakdown of red blood cells (RBCs), releasing hemoglobin. It has two types:

• Extravascular hemolysis – Normal process; macrophages in the spleen remove old RBCs.

• Intravascular hemolysis – Pathological; free Hb is released into plasma, leading to hemoglobinemia and possible hemoglobinuria.

What happens to hemoglobin after RBC breakdown?

• Globin → Broken down into amino acids

• Iron (Fe) → Recycled and stored

• Heme → Converted into bilirubin in the liver

What is intravascular hemolysis, and what can it cause?

• A pathological process that releases free Hb into plasma (hemoglobinemia).

• Filtered by kidneys, leading to hemoglobinuria.

• Hb resorption in renal tubules may cause hemoglobinuric nephrosis (kidney damage).

What are some causes of intravascular hemolysis?

• Immune-mediated hemolysis

• Toxins (e.g., snake venom, oxidative damage)

• Infectious agents (e.g., Babesia)

• Mechanical damage (e.g., hemolytic anemia, burns)

What is haemosiderin?

A yellow-brown pigment that stores iron, formed from the breakdown of hemoglobin. It is an insoluble storage form of iron and can accumulate in macrophages.

Where is haemosiderin normally found?

In small amounts in macrophages of the spleen, liver, and bone marrow.

What stain is used to identify haemosiderin?

Prussian blue stain, which specifically detects iron deposits.

What are heart failure cells?

Macrophages in the lungs containing haemosiderin, seen in congestive heart failure due to chronic pulmonary congestion.

What are some causes of haemosiderosis?

• Excessive hemoglobin breakdown (e.g., hemolytic anemia)

• Repeated blood transfusions

• Excessive dietary iron absorption

• Impaired iron metabolism (e.g., in certain bird species like toucans, mynah birds, and black rhinos)

What is bilirubin, and how is it formed?

• Bilirubin is an orange pigment derived from hemoglobin breakdown.

• It forms when iron and globin are removed from hemoglobin.

• It circulates in the bloodstream loosely bound to albumin and is eventually excreted via bile into the feces.

What are the two main forms of bilirubin, and how are they processed in the liver?

1. Free (Unconjugated) Bilirubin

   • Bound to albumin in the plasma.

   • Insoluble in water, requiring transport to the liver.

2. Conjugated Bilirubin

   • Hepatocytes take up free bilirubin and conjugate it with glucuronic acid.

   • This process makes bilirubin water-soluble, allowing excretion via bile into the intestines.

What happens to bilirubin once it enters the intestines?

• Conjugated bilirubin is excreted into bile and enters the small intestine.

• In the colon, gut bacteria deconjugate bilirubin, converting it to urobilinogen (a colorless compound).

• Urobilinogen follows three pathways:

  1. Some is oxidized to stercobilin (which gives feces its brown color).

  2. A portion is reabsorbed into the bloodstream, returned to the liver, and reused (enterohepatic cycling).

  3. A small amount is excreted in urine as urobilin, which gives urine its yellow color.

What is jaundice (icterus), and what causes it?

• Jaundice is a condition where excess bilirubin accumulates in the blood, leading to yellow discoloration of the skin, sclera (eyes), and mucous membranes.

• The bilirubin source can be pre-hepatic, hepatic, or post-hepatic, depending on the underlying cause.

• Jaundice is easiest to observe in areas like the gums, eyes, and inguinal (groin) region.

What are the three types of jaundice, and what causes each?

1. Pre-hepatic (Hemolytic) Jaundice

   • Occurs when there is increased RBC breakdown, leading to excess free bilirubin in the blood.

   • Causes include:

     • Immune-mediated hemolytic anemia (IMHA)

     • RBC parasites (e.g., Haemobartonella, Babesia)

     • Leptospirosis (some strains release exotoxins that cause hemolysis)

     • Neonatal jaundice (e.g., Rhesus incompatibility in foals)

     • Chronic copper poisoning

2. Hepatic (Toxic) Jaundice

   • Caused by liver damage, reducing the liver’s ability to conjugate and excrete bilirubin.

   • Leads to increased free bilirubin in the blood.

   • Causes include:

     • Leptospirosis

     • Ragwort poisoning

     • Chronic copper poisoning

3. Post-hepatic (Obstructive) Jaundice

   • Results from blockage of the bile ducts, preventing bilirubin excretion.

   • Leads to increased conjugated bilirubin in the blood.

   • Causes include:

     • Gallstones, tumors, parasites, inflammation, scarring

     • Secondary to toxic jaundice

     • Rupture of the bile duct

What are the consequences of pre-hepatic (hemolytic) jaundice?

• Increased free (unconjugated) bilirubin in the blood.

• Can be toxic to neurons at high concentrations.

• May cause anemia due to excessive RBC destruction.

• Hemoglobinemia & hemoglobinuria may occur if hemolysis is intravascular (RBCs rupture within circulation).

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What are the consequences of post-hepatic (obstructive) jaundice?

• Increased conjugated bilirubin in the bloodstream.

• Reduced serum and urine urobilinogen due to blockage.

• Pale feces if bile flow is completely obstructed, since stercobilin (which colors feces brown) is absent.

What are porphyrins, and where are they found?

• Porphyrins are essential components of:

  • Haemoglobin (Hb) – oxygen transport

  • Myoglobin (Mb) – oxygen storage in muscles

  • Cytochromes – involved in cellular respiration

What happens in inherited porphyrin metabolism defects?

• Defects occur in humans and cattle (e.g., uroporphyrinogen III cosynthase defect).

• Porphyrins accumulate in teeth and bones, causing:

  • Pink discoloration

  • UV fluorescence

  • Photosensitization (skin damage when exposed to light)

What is amyloid, and where is it found?

• Amorphous, eosinophilic material composed of glycoprotein fibrils arranged in β-pleated sheets.

• Found between cells and beneath basement membranes, interfering with organ function.

• Common sites: liver, kidney, pancreas.

• Stains with Congo Red and exhibits green birefringence under polarized light.

What are the main causes of amyloidosis?

• Derived from specific proteins, associated with:

  1. Chronic inflammation → Serum Amyloid A (AA protein)

     • Acute phase protein, produced by hepatocytes

     • Most common form in veterinary medicine

  2. Antigen-Antibody (Ag-Ab) reactions → Immunoglobulin light chains (AL protein)

     • More common in humans, linked to multiple myeloma

     • Rare in horses and dogs

What are examples of amyloidosis in different species?

• Cats → Renal medullary interstitium (common in Abyssinian cats, Shar-Pei dogs)

• Dogs → Renal glomeruli

• Horses → Nasal submucosa

• Marmosets → Splenic germinal centers

• Ducks → Liver

• Feline diabetes → Amyloid deposition in pancreatic islets

How does renal amyloidosis affect kidney function?

• Amyloid deposits in glomeruli, causing "leakiness".

• Leads to protein loss in urine (proteinuria).

• Chronic kidney damage due to impaired filtration.

How is amyloid involved in Alzheimer's disease?

• Amyloid-β (Aβ) plaques accumulate around neurons in the CNS.

• Leads to neurodegeneration and cognitive decline.

• Some Aβ fragments are excreted into urine.

Where is glycogen normally found, and what is its function?

• Normally present in liver and muscle.

• Serves as a storage form of glucose, providing energy when needed.

What conditions lead to excessive glycogen accumulation?

• Defective glucose or glycogen metabolism, as seen in:

  • Diabetes mellitus

  • Glycogen storage diseases

How does glycogen accumulation affect cells?

• Intracellular glycogen attracts water osmotically, leading to hydropic degeneration (cell swelling).

• Affected organs/tissues include:

  • Hepatocytes (liver)

  • Myocardium (heart muscle)

  • Renal epithelium (kidney)

What is melanin, and where is it found?

• Black pigment produced by melanocytes.

• Found in skin, hair, iris, and choroid.

• Released from melanocytes into the epidermis and macrophages.

• Fontana-Masson stain is used to identify melanin.

What factors influence melanin production?

• Genetic variation leads to different skin and hair colors.

• Freckles result from localized hyperpigmentation.

• Hormonal, nutritional, and environmental factors can alter pigmentation

What are some causes of decreased melanin?

• Congenital hypopigmentation (Albinism):

  • Genetic condition with tyrosinase deficiency.

  • Red/pink irises due to lack of melanin.

• Acquired hypopigmentation:

  • Hormonal imbalance

  • Trauma (e.g., freeze branding)

  • Copper deficiency

  • Vitiligo: Autoimmune loss of melanin in pigmented skin.

What are some causes of increased melanin?

• Suntan: Increased melanin due to UV exposure.

• Moles (Nevi): Localized benign melanin overproduction.

• Melanoma: Malignant tumor of melanocytes.

• Environmental melanosis: Pigment accumulation from environmental factors.

• Congenital melanosis:

  • Due to embryonic displacement of melanocytes.

  • Seen in Black-faced sheep (Suffolk, BBB) and certain pig breeds (Duroc, St. Clair).

What are lipopigments, and what are their key features?

• Large heterogeneous group of pigments.

• Contain fat and sugars.

• Yellow-brown color.

• Fluoresce under UV light.

• Found in lysosomes, not cytoplasm.

• Associated with aging, fat oxidation, and heavy metals.

What is lipofuscin, and how does it relate to aging?

• Also known as age pigment or wear-and-tear pigment.

• Found in small amounts in young cells, increases with age.

• Accumulates in non-dividing cells (neurons, cardiac myocytes, hepatocytes).

• May result from lipid peroxidation of cell membranes.

• Harmless, but its presence signifies aging.

What is the pigment of brown atrophy?

• Occurs in aged cattle.

• Causes brown discoloration of heart and skeletal muscle.

• Incidental finding at slaughter → meat condemned.

• Likely genetic in origin.

What is ceroid, and how does it differ from lipofuscin?

• Pathological pigment linked to lipid degeneration.

• Unlike lipofuscin, ceroid has deleterious effects on cells.

• Found in necrotic fat, brain necrosis, fatty liver.

• Process accelerated by iron.

What diseases and conditions involve ceroid accumulation?

• Brown gut disease (dogs): Affects tunica muscularis (smooth muscle cells).

• Yellow fat disease (nutritional steatitis):

  • Birds, reptiles, ferrets.

  • Associated with diets high in unsaturated fats & low in vitamin E.

  • Oxidized rancid fats deplete vitamin E, worsening the condition.

• Ceroid-lipofuscinoses:

  • Inherited storage diseases in humans, sheep, goats, cattle, cats, dogs.

  • Affects neurons, leading to retinal and brain atrophy.

  • Identified using Oil Red O, Sudan Black stains.

Where is cholesterol deposition seen in tissues, and what are its effects?

• Found in areas of chronic tissue damage or hemorrhage.

• Forms characteristic clefts (cholesterol crystals dissolve during tissue processing).

• Induces foreign body giant cell formation.

• Seen in atheromatous plaques in humans.

What is gout, and what causes it?

• Deposition of uric acid or urates in tissues.

• Clinically significant in joints.

• Affects humans and birds (articular/pericardial gout), cats, and dogs.

• Crystals initiate a foreign body reaction.

• Associated with impaired urate or purine metabolism due to:

  • Renal failure.

  • Inherited metabolic diseases.

What is anthracosis, and how does it affect the lungs?

• Accumulation of carbon in lungs and respiratory lymph nodes.

• Results from chronic inhalation of soot.

• Harmless, but causes dark tissue discoloration.

• Seen in coal miners ("coal-miner's lung").

What happens to tattoo pigments in the skin?

• Pigments injected into the dermis.

• Remain permanent because dermal cells do not shed like epidermal cells

How do tetracyclines affect tissues?

• Antibiotic with a yellow pigment.

• Potent calcium chelators → precipitate in mineralized tissues (bone, teeth).

• Causes yellow/brown discoloration of teeth and bones.

How does chronic copper poisoning affect the liver?

• Dusky brown pigment accumulates in hepatocytes.

• Detected using rhodanine stain.

What is carotene pigment, and where is it stored?

• Yellow pigment stored in fat.

• Normal finding in:

  • Horses.

  • Jersey cows.

  • Certain monkeys (Red Howler).

  • Birds (Scarlet Ibis, Flamingo).